This invention relates to an EUV (Extreme Ultraviolet) radiation source used for a light source of a semiconductor exposure apparatus etc.
A reduction exposure apparatus is used to manufacture a semiconductor circuit having fine patterns. Conventionally, an X-ray reduction exposure apparatus is used therefor. For example, in Japanese Laid Open Patent No. 9-115813, an exposure apparatus in which an X-ray generating apparatus is use is disclosed.
In the exposure apparatus, an X-ray source, an illumination optical system, a mask, and wafer etc. as a whole are contained a vacuum container that is kept vacuous. An X-ray from the X-ray source is irradiated on a mask on which a circuit pattern is formed and the image of the mask is reduced and projected on the wafer, so that resist disposed on the wafer surface is exposed and the circuit pattern is transferred.
In recent years, as a semiconductor integrated circuit becomes smaller and smaller, shorter wave length light is required. As a short wave length light source, a KrF laser source (248 nm) and an ArF laser source (193 nm) have been developed. A 50 nm EUV lithograph that is so-called the last lithography of a Si device is being developed.
A light source for the EUV lithography irradiates EUV radiation whose wavelength is about 10 to 13 nm. Discharge plasma is used to irradiate an EUV radiation having an about 10 to 13 nm wavelength.
In Japanese Laid Open Patent No. 2001-42098, a plasma focus type EUV radiation source is disclosed. Further, in U.S. Pat. No. 6,188,076, and WO 01/97575 specification, an EUV radiation source in which a capillary discharge is used is disclosed. All of the EUV radiation generating apparatuses described above, generate EUV radiation by generating high temperature and high density plasma by discharge.
As shown in FIG. 6 (a schematic diagram), in a semiconductor exposure apparatus in which an EUV radiation source is used, the EUV radiation source 1 in which capillary discharge is used, a light condensing mirror 2 having multi-layer films on a reflecting surface thereof, a reflecting type mask 3, a projection optical system 4, wafer 5 etc. are contained in a vacuum container. EUV radiation is condensed by the condensing mirror 2 and then is emitted to the reflecting type mask 3. The reflected light from the reflecting type mask 3 is reduced and projected on the surface of the wafer 5 via the projection optical system 4.
FIG. 7 shows an example of conventional EUV radiation source in which capillary discharge described above is used and is a cross sectional view taken along a plan containing the optical axis of the EUV radiation irradiated from the EUV radiation source.
As shown in FIG. 7, the capillary structure 21 is disposed, for example, between a first electrode 11 (a high voltage side electrode) made of tungsten and a second electrode 12 (a ground side electrode ) made of tungsten. The capillary structure 21 is an insulated cylinder made of, for example, silicon nitride. The capillary structure 21 has a 3 mm diameter capillary 21 at the center of the capillary structure 211.
The first and second electrodes 11 and 12 are electrically connected to a power supply (not shown) via leads 31 and 32, and high voltage pulse is applied between the first and second electrodes 11 and 12 from the power source. The second electrode is usually grounded, and for example negative high voltage pulse is applied to the first electrode 11. (Hereinafter refer to the first electrode and the second electrode as a high voltage side electrode and a ground side electrode, respectively.)
The high voltage side electrode 11 has a through hole 111 and the ground side electrode 12 has a through hole 121. These through holes and the capillary 211 of the capillary structure 21 are on the same axis.
An insulated plate 73 is provided on the ground side electrode 11. The insulated plate 73 is fixed on a partitioning cylinder 71 and further the partitioning cylinder 71 is fixed on a bottom plate 72. Thus, a closed space Sa is defined by the high voltage side electrode 11, the insulated plate 73, the partitioning cylinder 71 and the bottom plate 72.
On the bottom plate 72, through holes in which the leads 31 and 32 are provided, a gas introducing inlet 4115 for introducing gas into the space Sa, an exhaust port 42 are provided. Actuating gas, for example xenon, is introduced from the gas introducing inlet 41 and discharged from the exhaust port 42 so that pressure in the closed space Sa is controlled so as to be appropriate.
The bottom plate 72 and an outside cylinder 81 are air-tightly joined and define a space Sb isolated from the outside. An exhaust port 82 is provided on the outside cylinder 81.
The actuating gas in the closed space Sa flows out to the space Sb via the through holes 111 and 121 formed in the electrodes 11 and 12 and the capillary 211, and then it is discharged from the exhaust port 82. The inside of the isolated space Sb is maintained in a vacuum condition by increasing displacement from the exhaust port 82.
In FIG. 7, when a high voltage pulse is applied to the ground side electrode 12 and the high voltage side electrode 11 while the actuating gas is introduced to the though holes 111 and 121 and the capillary 211, gas discharge takes place inside the capillary 211, and high temperature plasma is formed. Thereby, EUV radiation having 10 to 13 nm wavelength is generated. The EUV radiation is irradiated into the space Sb kept in a vacuum condition.
As described above, the EUV radiation source generates EUV radiation by gas discharge generated by impressing high voltage pulse. When electric input energy is 10 J per pulse and 1,000 pulses are impressed, the total energy is 10,000 W.
That is, to increase power of light emitted from the EUV radiation source, the electric input energy per one pulse should be increased or the number of impressed pulses per unit time should be increased. The larger the power of the EUV radiation irradiated from the EUV radiation source is, the more advantageous it is for the throughput of an exposure process to be improved.
As described above, to increase the power of the EUV radiation irradiated from the EUV radiation source, the electric input energy per one pulse or the number of pulses applied per unit time must be increased. In either way, the increase of power of the light emitted from the EUV radiation source raises temperature of the EUV radiation source comprising the high voltage side electrode 11, the ground side electrode 12 and the capillary 21. As a result, toxic dust (hereinafter referred to as debris) is generated since the temperature of the capillary structure 21 opposed to the center of the discharge plasma where the temperature increases most, increases, and the surface of the capillary structure 21 is evaporated.
The generated debris becomes an obstacle to transmission of the EUV radiation. The debris is deposited on the surface of the reflecting mirror of the exposure optical system, thereby, the reflectance of the reflecting mirror decreases. Thus, credibility and performance of the exposure apparatus is impaired by the debris.
The high voltage side electrode 11 and the ground side electrode 12 are made of tungsten therefore they are not evaporated readily, but if the temperature extremely highly increases, they are evaporated and debris is generated as well as the capillary structure 21.
It is an object of the present invention to provide an EUV radiation source capable of irradiate EUV radiation of a large power, minimizing debris.
The present invention provides an EUV radiation source comprising, a first electrode having a first through hole, a second electrode having a second through hole, a movable insulator, having a plurality of third through holes, provided between the first and second electrodes, wherein actuating gas is introduced in the first, second through holes and one of the plurality of third through holes, and voltage is impressed between the first and second electrodes when the first, second and plural through holes are located on a common axis.
The insulator may be disciform.
The insulator may be rotated with respect to a point.
The plurality of third through holes may be concentrically provided.
The EUV radiation source may include an ultraviolet laser source to generate pre-plasma.
The present invention also provides an EUV radiation source, comprising a first electrode having a first through hole, a second electrode having a plurality of second through holes, a movable insulator having a plurality of third through holes, each of which is connected to one of the plurality of second through holes, wherein the second electrode and the insulator are integrally provided, and wherein actuating gas is introduced in the first hole, one of the plurality of second through holes and one of the plurality of third through holes connected to the one of the plurality of second through holes, and voltage is impressed between the first and second electrodes when the first through hole, the one of the plurality of second through holes and the one of the plurality of third through holes are located on a common axis.
The first electrode and the insulator may define a hollow portion therein for passing through coolant.
The EUV radiation source may include an ultraviolet laser source to generate pre-plasma.